1. Field of the Invention
This invention relates to an electromagnetically controlled spring clutch mechanism for transmitting a driving force by utilizing contraction of a coil spring means.
2. Description of the Prior Art
Electromagnetically controlled spring clutch mechanisms utilizing a coil spring means have previously been used widely to transmit selectively the driving force of an input rotating element being driven. One example of clutch mechanisms of this type is disclosed in U.S. Pat. No. 4,570,768. The present applicants proposed an improvement of the known clutch mechanism and disclosed it in the specification and drawings of U.S. Pat. No. 4,704,554 (entitled: ELECTROMAGNETICALLY CONTROLLED SPRING CLUTCH MECHANISM). The improved electromagnetically controlled spring clutch mechanism comprises an output rotating element mounted rotatably, an input rotating element mounted on the output rotating element, a rotor adapted to rotate as a unit with the output rotating element, an armature positioned opposite to one side surface of the rotor, a rotating supporting member mounted rotatably on the output rotating element, a biasing spring member interposed between the armature and the rotating supporting member for elastically biasing the armature away from said one side surface of the rotor, an electromagnetic means for magnetically attracting the armature to said one side surface of the rotor against the elastic biasing action of the biasing spring member, a first boss member adapted to rotate as a unit with the input rotating element, a second boss member adapted to rotate as a unit with the output rotating element, and a coil spring means fitted over and across the first and second boss members with one end being connected to the input rotating element and the other end being connected to the rotating supporting member. When the electromagnetic means is energized, the armature is attracted to said one side surface of the rotor by the electromagnetic attracting force of the electromagnetic means. This produces a difference in speed between the input rotating element and the rotating supporting member, and the coil spring means is contracted. As a result, the first boss member and the second boss member are drivingly connected via the coil spring member. On the other hand, when the electromagnetic means is deenergized, the armature is moved away from the one side surface of the rotor by the elastic biasing action of the biasing spring member, whereby the contraction of the coil spring means is cancelled. This results in releasing of the driving connection of the first and second boss members via the coil spring means.
The aforesaid electromagnetically controlled spring clutch mechanism has such a structure that while the electromagnetic means is energized, the driving connection is achieved and the driving force is transmitted. It is difficult therefore to control the mechanism accurately so that the output rotating element is rotated through a predetermined angle. To rotate the output rotating element through a predetermined angle, for example through 180.degree., it is proper in principle to deenergize the electromagnetic means when the output rotating element has rotated through the predetermined angle (e.g., 180.degree.). It is difficult, however, to rotate the output rotating element accurately through the predetermined angle owing to the difficulty of accurately detecting the rotating angle of the output rotating element, and to the response characteristics of the clutch itself. There exists a spring clutch mechanism in which the output rotating element is rotated through a predetermined angle. Such a spring clutch mechanism is composed of a spring clutch means and an actuation controlling means annexed to the spring clutch means. The spring clutch means has an output rotating element mounted rotatably, an input rotating element mounted rotatably on the output rotating element, a first boss member adapted to rotate as a unit with the input rotating element, a second boss member adapted to rotate as a unit with the output rotating element, a coil spring means fitted over and across the first and second boss members, and a ratchet having a pawl portion and fitted over, and rotatably mounted on, the coil spring means, one end of the coil spring means being connected to the ratchet and its other end being connected to the second boss member. The actuation control means has an actuation control member having an engaging pawl engageable with the pawl portion of the ratchet, and an actuation means, such as an electromagnetic solenoid, for actuating the actuation control member. When in this spring clutch mechanism, the actuating means is in the deenergized state, the engaging pawl of the actuation control member is in engagement with the pawl portion of the ratchet, the rotation of the ratchet incident to the rotation of the input rotating element is accurately hampered and the contraction of the coil spring means is hampered. As a result, the first and second boss members are not drivingly connected through the coil spring means. On the other hand, when the actuating means is energized and the engaging pawl is disengaged from the pawl portion of the ratchet, the ratchet is rotated incident to the rotation of the input rotating element whereby the coil spring means is contracted. As a result, the first and second boss are drivingly connected via the coil spring means as is required.
The spring clutch mechanism of the described construction, however, requires a space for installing the actuation control means together with the spring clutch means. It further has the disadvantage that it is difficult, and time-consuming, to prescribe the relative positions of the spring clutch means and the actuation control means, particularly the relative positions of the pawl portion of the ratchet and the engaging pawl of the actuation control means.